The present invention relates to a combined cycle power plant and, more particularly, to a combined cycle power plant in which iron oxides in condensate of a condenser or iron oxides in drum water of an exhaust heat recovery boiler can be effectively removed.
A conventional combined cycle power plant provided with an apparatus for removing iron oxides in condensate is disclosed in Japanese patent publication JP-B-63-59006 (1988). In the conventional plant, a gas turbine is supplied with fossil fuel and air to burn the fuel and driven by a high temperature combustion gas to rotate a generator thereby to effect a first stage power generation. Next, a high temperature exhaust gas from the gas turbine is fed to a boiler in which steam is generated, and the exhaust gas having been lowered in temperature through the generation of the steam is exhausted. The steam is fed to a steam turbine to drive it and to effect a second stage power generation by a generator connected to the steam turbine. Subsequently, an exhaust steam from the steam turbine is sent to a cooler in which the steam is caused to contact indirectly with a cooling water and cooled to be condensate. The condensate is fed to the boiler by a feed pump through a condensate demineralizer which employs H type cation exchange resin and OH type anion exchange resin. The condensate is treated of by the condensate demineralizer.
The conventional combined cycle power plant is constructed so that all the condensate to be fed to the boiler passes through the condensate demineralizer. Therefore, the total pump head of the feed pump increases, and power consumption of the feed pump also increases. Further a larger capacity demineralizer is required in this case because all the condensate to be fed to the boiler passes through the demineralizer.
In another conventional combined cycle power plant, a condensate recirculation line for recirculating a condensate in a condenser and a blow off line for removing iron oxides from feed water or condensate is provided in a condensate feed line for feeding condensate from a steam turbine to an exhaust heat recovery boiler at a downstream side of a feed pump mounted on the condensate feed line. At starting time of the power plant, the concentration of oxygen dissolved in the condensate is high, about several thousand ppb; the condensate can not be fed to the exhaust heat recovery boiler without any treatment of the condensate. Therefore, deaeration of the condensate is effected to the extent that requirement of the exhaust heat recovery boiler is satisfied, by recirculating the condensate from the condenser to the condenser through the condensate recirculation line and heating the condensate in the condenser with auxiliary steam fed to the condenser through an auxiliary steam line.
In this power plant, iron oxides in the condensate are removed by blowing off a part of condensate. For example, in the combined cycle power plant of around 1000 MW, a condensate of about 80 m.sup.3 is blown off for about 50 minutes at the start up of the plant. The condensate blown off is compensated by introducing make-up water into the condenser. As a result, a reduction effect of the dissolved oxygen is lowered by the introduction of the auxiliary steam, which results in increasing of the starting time of the power plant.